столбец по убыванию в матрице

#include <iostream>
using namespace std;
int main()
{
    int N, M;
    cin >> N >> M;
    int** arr=new int* [N];
    int Z;
    for (int i = 0; i < N; i++)
        arr[i] = new int[M];

    for (int i = 0; i < N; i++) {
        for (int j = 0; j < M; j++)
            cin >> arr[i][j];
    }
    cin >> Z;
        cout << endl;

        for (int i = 0; i < N - 1; i++) {
            if (arr[i][Z] <= arr[i + 1][Z]) {
                int temp = arr[i][Z];
                arr[i][Z] = arr[i + 1][Z];
                arr[i + 1][Z] = temp;
            }
        }
        for (int i = 0; i < N; i++) {
            for (int j = 0; j < M; j++)
                cout << arr[i][j] << " ";
            cout << endl;
    }
}